A vehicle that uses liquefied gas fuel such as liquefied petroleum gas (LPG) is conventionally known. In this type of vehicle, the liquefied gas fuel is injected from a fuel injection valve to a combustion chamber, and the non-injected surplus fuel is returned to a fuel tank as a return fuel.
Patent document 1 discloses a vehicle including an air conditioning system that cools the air blown into a vehicle compartment, and a fuel cooling device that cools the return fuel using a part of a cooling medium of the air conditioning system. In the air conditioning system, the air introduced into the vehicle compartment is cooled using a refrigerating cycle. In other words, the air passing through an evaporator is cooled using a vaporization heat of when the cooling medium compressed by a compressor is vaporized by the evaporator. The cooled air is introduced into the vehicle compartment.
The fuel cooling device includes a branched passage branched from a circulating path of the cooling medium of the air conditioning system, and a throttle valve arranged on the branched passage. The throttle valve adjusts the amount of cooling medium flowing through the branched passage. A fuel cooling unit is arranged on the branched passage. The cooling medium supplied to the fuel cooling unit cools the return fuel through heat exchange.
In the device described in patent document 1, the compressor is driven and the cooling medium is supplied to the fuel cooling device when a pressure in the fuel tank becomes greater than or equal to a predetermined pressure while the compressor is stopped. The return fuel is thereby cooled and then returned to the fuel tank, whereby the temperature in the fuel tank lowers. The pressure in the fuel tank thus lowers, and the refilling of fuel to the fuel tank can be realized.
Furthermore, in this type of vehicle, the amount of fuel supplied to the fuel injection valve cannot become deficient with respect to the amount of fuel injected from the fuel injection valve. Thus, the fuel in which a predetermined amount is added in extra to the injection amount is supplied to the fuel injection valve. As a result, the fuel of an amount substantially equal to the predetermined extra amount is returned to the fuel tank as the return fuel. In this case, the amount of return fuel is set based on the fuel injection amount. Thus, in the device described in patent document 1, the fuel of an amount substantially equal to the predetermined extra amount is constantly returned to the fuel tank as the return tank. If the predetermined extra amount is small, therefore, the fuel tank is less likely to be cooled even if the return fuel is cooled since the amount of low temperature fuel returned to the fuel tank is small. Thus, a considerable time is required until the refilling of fuel to the fuel tank is enabled. If the predetermined extra amount is large, on the other hand, the return fuel is returned to the fuel tank even though the return fuel is not sufficiently cooled. In this case, the return fuel receives the heat of the internal combustion engine and becomes a high temperature. Thus, if a large amount of high temperature return fuel is returned to the fuel tank, the temperature in the fuel tank may rise.